The invention relates to a stable energy-saving lamp. A lamp cap (1) and an upper cover (2) are fixed together; the upper cover (2) and a lower cover (3) are fixed together; an inclined interface (31) is formed on the lower cover (3) to be matched with an upper end interface (52) of an energy-saving lamp tube (5); the lower cover (3) is fixedly provided with a circuit board box (6) in a screw connection manner; a circuit board (4) is fixed in the circuit board box (6); the energy-saving lamp tube (5) is a spiral energy-saving lamp tube and is provided with an accommodating space (51); and the circuit board box (6) is inserted in the accommodating space (51). The volume and the length of the energy-saving lamp can be reduced and meanwhile the stability of the energy-saving lamp tube is improved.